A conventional train wireless system, which performs traffic control on the basis of an interval between a train and another train preceding or following the train, needs to grasp the lengths and positions of the respective trains. The train wireless system can set a train length to a fixed value when the train has the fixed number of vehicle. However, the train wireless system encounters a problem in setting a length of a train such as a freight train whose number of vehicles of the train varies. When a train driver or a command person manually sets a train length on the basis of the number of vehicles, the mistake in inputting the train length may cause an accident such as collision of trains. With respect to the above problem, Patent Literature 1 below discloses technique for calculating a length of a travelling train by multiplying the velocity of the train by a travelling time during which the train travels.